Question 8
Back to Exercise
How many solutions in non-negative integers does x + y + z + w = 20 have if x ≥ 2?
- A 1,771
- B 1,540
- C 1,330 Correct
- D 969
Correct Answer: Option C
Let x = 2 + x′: x′ + y + z + w = 18
(18 + 3)C3 = 21C3 = 1,330
Trap: 1,771 = 23C3 ignores x ≥ 2.
Answer: 1,330
Discussion & Comments 0
Share your method, a shortcut, or ask about a step you didn't follow.
No comments yet. Be the first to share your solution!